    Patent Document 1: Japanese Patent Application Laid-Open No. 11-283664    Patent Document 2: Japanese Patent Application Laid-Open No. 2000-164252    Patent Document 3: Japanese Patent Application Laid-Open No. 2001-126758    Patent Document 4: Japanese Patent Application Laid-Open No. 2000-285910
In recent years, there have been remarkable advances in electronic technology, in which portable electronic devices have been designed to be smaller, lighter, thinner, and more multi-functional. With this, batteries serving as power sources for electronic devices have been strongly required to be smaller, lighter, and thinner and to have improved reliability. To meet these requirements, there has been proposed a multilayer lithium ion secondary battery in which positive electrodes and negative electrodes are stacked with solid electrolyte layers interposed therebetween. Such a multilayer lithium ion secondary battery is assembled by stacking several tens μm thick battery cells, so that the battery can be easily reduced in size, weight, and thickness. In particular, a parallel-type or series-parallel-type multilayer battery is superior in the ability to achieve a large discharge capacity even in a small cell area. An all-solid-state lithium ion secondary battery, which is produced using a solid electrolyte in place of a liquid electrolyte, does not have the risk of liquid leakage or liquid depletion and is highly reliable. Such a lithium-based battery can also produce high voltage and high energy density.
FIG. 8 is a cross-sectional view of the basic structure of a conventional, all-solid-state lithium ion secondary battery. A conventional, all-solid-state, lithium ion secondary battery has a basic structure where a negative electrode layer 103 made of a negative electrode active material, a solid electrolyte layer 102, and an positive electrode layer 101 made of a positive electrode active material are stacked in this order. Such a conventional, all-solid-state, lithium ion secondary battery has a problem that its ion conductivity is lower than that of a liquid electrolyte-based lithium ion secondary battery and its resistance of the interface between the electrolyte layer and the positive and negative electrode layers is high, resulting in a difficulty in increasing the battery capacity.
Patent Document 1 discloses a battery having one or more intermediate layers that are placed between a solid electrolyte layer and a positive electrode layer and/or a negative electrode layer and composed of 5 to 95% by weight of an active material and 5 to 95% by weight of a solid electrolyte. It suggests that the intermediate layer can reduce the polarization resistance of the interface between the electrode and the solid electrolyte so that battery characteristics such as charge-discharge characteristics and energy density can be improved.
Patent Document 2 discloses a battery having an intermediate layer that is placed between a solid electrolyte and an electrode active material and has a reaction interface between the solid electrolyte and the electrode active material. Similarly to Patent Document 1, it suggests that the intermediate layer can reduce the polarization resistance of the interface between the electrode and the solid electrolyte so that battery characteristics such as charge-discharge characteristics and energy density can be improved.
In practice, however, batteries manufactured by the techniques described in Patent Documents 1 and 2 have a problem that a significant reduction in internal resistance or an increase in battery capacity cannot be achieved.